Project Summary Adolescent and young adult men who have sex with men (YMSM) are the only group in the U.S. where rates of new HIV infections are increasing, which reflects a large disparity relative to heterosexuals. Steady or main partner relationships account for a substantial proportion of new HIV infections in YMSM. Among YMSM a serious relationship status is perhaps the strongest predictor of condomless anal intercourse (CAI), and pre- exposure prophylaxis (PrEP) may also be discontinued in a relationship. Alcohol and drug use are important influences on HIV risk in YMSM, particularly in serious relationships. Romantic relationships also provide myriad benefits, including promotion of mental, behavioral, and physical health. Despite the critical importance of romantic relationship factors for HIV prevention, the vast majority of studies and interventions focus on individuals. My research team and I conducted formative research on coupled YMSM through an NIH R21 from which I developed an innovative couples-based intervention that addresses the continuum of HIV prevention and care for YMSM couples. The 2GETHER program integrates couples- and group-based modalities and is innovative in its design to address HIV transmission risk in couples regardless of serostatus; couples learn to utilize behavioral and biomedical approaches to prevent both HIV acquisition and transmission, with an overarching emphasis on improving relationship functioning. 2GETHER further encourages uptake of couples- based HIV testing for HIV-/unknown YMSM and addresses medication adherence and barriers to care for HIV+ YMSM. I established feasibility, acceptability and preliminary efficacy 2GETHER in a pilot trial of coupled YMSM (N=52 couples; 104 individuals), including significant decreases in HIV transmission risk behavior. My pilot focused primarily on prevention of risk behavior, and given its highly promising effects, I now take an important scientific risk to also evaluate its effects on engagement in care. I propose to test the efficacy of 2GETHER in a comparative effectiveness RCT relative to existing public health practice (PHP). I will: (a) enroll racially diverse coupled YMSM; (b) randomize couples to either the 2GETHER intervention or PHP (couples voluntary HIV counseling and testing for HIV- YMSM; Life-Steps HIV medication adherence for HIV+ YMSM); (c) measure intervention outcomes through 12 months post-intervention. Primary behavioral outcome: an individual-level transmission risk variable for both HIV+/- men calculated based on relative risk of sex acts (a traditional CAI outcome will also be examined). Primary biomedical outcome: Chlamydia/Gonnorhea incidence. Secondary outcomes: HIV incidence and HIV testing uptake (HIV- men), viral load (HIV+ men), and substance use problems and relationship functioning as these are mediators of HIV risk. In the context of increasing fatigue for HIV prevention, I believe a healthy relationships program for coupled YMSM presents an opportunity to reinvigorate HIV prevention. Further, in the era of treatment as prevention, we must develop transmission prevention strategies for MSM regardless of serostatus that address the full continuum of prevention and care.